1. Field of Use for the Invention
The present invention relates generally to cabling/wiring and cabling/wiring systems, and more particularly to a universal cabling/wiring system wherein the requirement for specific wire interconnections between first and second devices is accomplished through use of a programmable I/O module.
2. Description of the Related Art
Sensors and actuators are connected to electronic control systems by wire and cabling systems. Sensors carry information into the control system. Sensors enable the measurement of such values as temperature, pressure, flow, proximity and human input. In contrast, actuators produce the action of the control system. Actuators include solenoids that enable the flow of motive air or fluid, and relays that provide power to motors, fans and heaters. Together, sensors and actuators make up the input and output (I/O) devices of modern electronic control systems.
Prior art control systems connect to sensors and actuators by employing a multitude of different fixed-configuration electrical circuits. Multiple instances of a given electrical circuit are packaged into modules in order to facilitate connection to sensors or actuators. Prior art input/output systems therefore typically employ dozens of different modules that are either input or output types. In addition, each category—input and output—is further classified by whether it is sourcing or sinking, sometimes called positive logic and negative logic, or PNP and NPN. In addition, each category of input/output module is further classified by whether it handles on/off signals, commonly called digital signals, or continuously varying signals, commonly called analog signals. Thus, a given prior art control system for a certain industrial application will often have four or more fixed-configuration input/output modules, handling digital inputs, digital outputs, analog inputs and analog outputs. More than four modules might be required if signals are not all sourcing or all sinking or if analog signals are of different formats, such as voltage, current, and different magnitudes.
The fixed configuration input/output systems of the prior art have remained essentially unchanged since the first electronic input/output systems were introduced about forty years ago. Today, input/output products are advertised and promoted based upon how many digital inputs, digital outputs, analog inputs and analog outputs they possess. Only two minor improvements have been made, neither changing the fixed configuration nature of the prior art.
The first improvement seen in the prior art came from the computer industry where “buses” are used to transfer signals into and out of memory. See U.S. Pat. No. 3,795,901 to Boehm et al. which discloses a bi-directional memory bus. Buses are now used in personal computers—disk drives are connected to the computer with cables containing bi-directional data busses. Some board-level products have been sold that offer bi-directional data pins, but such systems are not configurable. However, there is a crude level of configurability in so far as the direction of the fixed configuration signals can be reversed.
The second improvement seen in the prior art has been the use of programmable gain amplifiers to handle different input voltage ranges for modules configured as analog inputs. See U.S. Pat. No. 5,327,098 to Molina et al. which discloses a refinement of a well known programmable gain amplifier that is capable of variously amplifying different levels of voltages to better match the analog-to-digital converter. This prior art provides an input channel that is an analog input configured for voltage. However, only the level of the voltage may be adjusted.
Therefore, there is still a need to be able to readily reconfigure the basic input/output circuit, and there is still a need for a fully configurable input that can accommodate more than just different voltage levels.
Inevitably, the systems of the prior art all require that the user of the input/output module connect, by wire or cable, their sensors or actuators to specific terminals or connector pins on the input/output module. As a result, standard cables cannot in general be used to hook up the sensors and actuators. Because there is no standard format for sensor and actuator wiring, the user of these prior art systems must configure the wiring of the sensor or actuator to match the fixed configuration format of the input/output module.
Other than applying long-used bi-directional data techniques and programmable gain amplifiers, the design of the prior art input/output systems has remained remarkably unchanged for more than 40 years. There is a need for fully configurable input/output channels.
In addition, the prior art input/output systems do not provide for power to be supplied to the sensor or actuator. One skilled in the art knows that power for sensors and actuators must be supplied by separate power wiring which is not a part of the input/output module wiring. Once again, the user of the prior art is required to design wiring systems that are not simply point-to-point. Rather than standard cables, the user must design wiring harnesses which are custom, often complex assemblies of multiple connectors and conductors.
FIGS. 1A-1D and 2A-2D depict four different sensors and actuators along with their respective input or output circuits. One skilled in the art recognizes that these sensors may be any of a wide variety of devices such as proximity, temperature or pressure sensors. Similarly, the actuators may be any of a wide range of actuators, such as solenoids, stepper motors and relays. FIG. 1A depicts a sensor which sources current to its output terminal and must be connected to an input module with an input circuit designed for sourcing sensors. FIG. 1B depicts an input circuit, as might be found inside a prior art input module, where the input circuit is designed to accept a signal from a sensor which sources current. FIG. 1C depicts a sensor which sinks current and must be connected to an input module with an input circuit designed for sinking sensors. FIG. 1D depicts an input circuit, as might be found inside a prior art input module, where the input circuit is designed to accept a signal from a sensor which sinks current. FIG. 2A depicts an actuator which must be connected to an output module with an output circuit designed for sinking loads. FIG. 2B depicts an output circuit which sinks current. FIG. 2C depicts a compound actuator made up of two solenoids, such as would be found in a pneumatic valve manifold. Such a compound actuator must be connected to an output module with an output circuit designed for sourcing loads. Note that this compound actuator requires only three conductors to be connected up in order to operate. FIG. 2D depicts an output circuit designed to source current to its output terminal.
The sensors, actuators and input/output circuits depicted in FIGS. 1A-1D and 2A-2D are a small sample of the universe of sensors, actuators and circuits. In a given machine or process, an engineer generally expects all four of these categories of devices to be part of an input/output system. In addition, if analog sensors and actuators are to be used, more categories of input/output circuits will be required.
Sensors and actuators are wired to input/output modules with cables and connectors. FIGS. 3A and 3B depict an actuator 80 with three conductors that are internally connected to the actuator. The conductors form what is commonly called a “pig tail”. The three conductors 68 grouped together are called a cable 68B. Herein, a group of conductors is referred to as a cable. In FIG. 3A, the conductors 68 have attached to them connectors 69B which are for plugging into mating connectors. In the example shown in FIG. 3B, the conductors 68 have no connectors and are suitable for connecting to terminal blocks, a common type of connector.
FIG. 4A depicts a situation in which mating connectors 69B and 71B are used on both ends of the conductor 68 to connect with connectors 69 and 71 on the device 80 and the input/output module 66, respectively. FIG. 4B depicts the situation in which a mating connector is attached to the device end of the conductor 68 whereas the input/output module end is connected with a terminal block connector. Thus, the prior art describes a number of wiring techniques for attaching sensors and actuators to input/output systems.
FIG. 5 is generally representative of the prior art input/output systems in use today in a wide variety of industries around the world. Whether in Programmable Logic Controllers (PLC's) or Distributed Control Systems (DCS), sensors as show in FIGS. 1A-1D are wired to input/output systems using the teaching of FIG. 5. Because the two sensors shown in FIG. 5 wired to the input/output system are not either both sourcing or both sinking, the prior art requires that two fixed-circuit input modules be used, one a pull-down module for use with the sourcing sensor and the other module a pull-up module for use with the sinking sensor. FIG. 5 shows that the prior art wiring systems require many more wires than needed to simply connect the sensors to the input modules. In this case, ten wires are required to connect six terminals, three on each of the two sensors. In addition, only one input is used on each of the two input modules. In general, the prior art approach results in poor utilization of the channels on the input/output modules.
Terminal blocks are the preferred wiring system for most PLCs and input/output modules because wire harnesses can become very complex. For example, FIG. 6 takes the wiring layout from FIG. 5 and makes it into a wire harness. Note that this harness is very complicated and is essentially a three-dimensional web of conductors. Although harnesses are sometimes used, especially in specialty applications such as airplanes and automobiles, harnesses are inflexible, difficult to design, handle and repair.
The prior art does no better with actuators. FIG. 7 depicts a system of two output modules connecting the two types of actuators of FIGS. 2A-2D. In order to demonstrate the limitations of the prior art, two typical actuator groups have been selected—one requiring a sourcing output and one requiring a sinking output. Therefore, two output modules are required to complete the system. As with the input circuit shown in FIG. 5, the output circuit of FIG. 7 requires ten conductors to connect six terminals of the two types of actuators. Similarly, only three of sixteen output channels on the two output modules of FIG. 7 are used and only two of sixteen input channels on the two input modules of FIG. 5 are used. This is an inefficient use of the I/O channels.
In FIG. 8, the wiring harness for the output circuit of FIG. 7 is shown. As noted for the input harness of FIG. 6, the harness of FIG. 8 is also complex. As discussed below, a major limitation of the prior art is that the harness of FIG. 6 is different from the harness of FIG. 8. A user of input/output systems must use two different harnesses. The fact that harnesses in general are unique and custom helps to explain why those skilled in the art prefer to use individual wires and terminal block connectors because the interconnections can be built piece-by-piece.
In conclusion, the prior art apparatus for connecting sensors and actuators to fixed configuration input/output modules results in systems that have unique wiring layouts that employ a large number of conductors and make poor use of input/output channels. These systems with large numbers of partially-utilized input/output modules are inefficient. The significance of these limitations of the prior art cannot be overstated. A major result of this poor efficiency and excess of conductors is that input/output systems tend to be centralized in order to make better use of the input/output module resources and to provide for enough space for the wiring, not to mention the labor required to perform the wiring. Despite the long-held goal by those skilled in the art of control system design to provide for more distributed input/output systems where the input/output modules are physically distributed so as to be closer to sensors and actuators, the limitations of the prior art tend to reduce the advantages of distributed input/output systems and encourage the use of older centralized input/output system designs. Therefore, there remains a need for I/O modules with fully configurable input/output channels.